The present invention provides compounds useful for the detection of the enzyme tripeptidyl protease I (TPP-1). The invention also provides methods of making such compounds, methods of using such compounds, and kits and compositions containing such compounds. In one embodiment, Gly-L-Pro-L-Ser-1-anthraquinonylhydrazide, in combination with p-anisaldehyde, is used to detect TPP-1.
Mutations in the CNL2 gene result in neuronal ceroid lipofuscinoses (NCL""s), a group of rare but devastating neurodegenerative diseases (Bennett et al., 1999). One type of NCL, known as classical late-infantile neuronal ceroid lipofuscinosis (LINCL), Jansky-Bielschowsky disease, CLN2 deficiency, or pepinase deficiency, presents as an acute seizure disorder at about 4-6 years of age, and includes rapid loss of visual, motor, and cognitive functions (Mole, 1998). Recent studies have shown that this disease is characterized by a deficiency in the soluble lysosomal protease tripeptidyl protease I (TPP-1; also known as tripeptidyl peptidase I or tripeptidyl aminopeptiase I) (Sleat et al., 1997), and that inactivating mutations of TPP-1 result in accumulation of storage material in the lysosome (Palmer, 1995). TPP-1 is a non-membrane bound lysosomal enzyme that can be secreted from cells over-expressing the enzyme, and taken up by deficient cells (Haskell et al., 2003). Thus, partial enzyme replacement will likely ameliorate the storage deficit.
Despite the increased understanding of the basis of this disease, current therapy for LINCL can only relieve the seizure disorder and cannot address the underlying cause or the progression of the disease (Bennett et al., 1999, Sleat et al., 1997). Furthermore, a major limitation in the development of gene-based therapies for neurodegenerative diseases, and more specifically TPP-1 deficiency, is assays to assess the distribution of the enzyme.
Thus, there is currently a need for additional substrates and methods useful for detecting TPP-1. For example, there is a need for additional substrates and methods that can provide specific information on TPP-1 distribution following enzyme replacement or gene transfer therapy.
Tripeptide derivatives of anthraquinones have been prepared and tested as histochemical reagents for detection of TPP-1. One compound, derived from 5-chloroanthraquinone hydrazide, was identified as a tetracyclic pyrazoanthrane based on analysis of 13C NMR data, while four others were tripeptide derivatives of the tricyclic anthraquinone hydrazide. The compound Gly-L-Pro-L-Ser anthraquinone hydrazide was the most effective histochemical reagent for detecting TPP-1, particularly when combined with p-anisaldehyde.
Thus, the present invention provides a compound of formula I: 
or a salt thereof, wherein
R is an anthraquinone, and
R1 is
(a) H, or
(b) C1-6alkyl.
A compound of formula I is Gly-L-Pro-L-Ala-1-anthraquinonylhydrazide, or a salt thereof.
The present invention also provides a compound of formula II: 
or a salt thereof.
A compound of formula II is Gly-L-Pro-L-Ala-5-chloro-1-anthra[1,9-cd]pyrozol-6(2H)-one, or a salt thereof.
The present invention further provides a compound of formula III: 
or a salt thereof, wherein
R is an anthraquinone, and
R1 is
(a) H, or
(b) C1-6alkyl.
A compound of formula III is L-Ala-L-Ala-L-Phe-1-anthraquinonylhydrazide, or a salt thereof.
The invention also provides compositions including compounds of the invention useful for detecting or determining TPP-1.
The invention further provides a method for detecting or determining TPP-i in a biological sample obtained from a mammal. In some embodiments, TPP-1 can be detected or determined following enzyme replacement or gene transfer therapy, for example, following virally-mediated gene transfer of a construct encoding TPP-1.
The invention also includes kits for carrying out the methods of the invention.
The invention also provides novel compounds, e.g., intermediates, and methods that are useful in preparing compounds of formula I, II or III.